Rick Santorum eked out a pair of pivotal victories in the Deep South on Tuesday night, winning hard-fought battles in Alabama and Mississippi that cement his standing as Mitt Romney’s chief challenger and could push Newt Gingrich out of the race.

With 86% of precincts reporting, Santorum notched 35% of the vote in Alabama, with Gingrich and Romney locked at 29%. He pulled out a three-way nail-biter in neighboring Mississippi, drawing 33% to 32% apiece for Gingrich and Romney. The result seemed to surprise even him. “We did it again,” he said with a note of shock in his voice as he stepped out to address supporters just before 11 p.m. In a sign that he outpaced even his own campaign’s expectations, Santorum had already skipped over to Louisiana, which votes next week. Candidates rarely pass up the chance for an on-site victory lap, but Santorum had never led in a Mississippi poll.

With tight victories in two states which allocate their combined 84 delegates proportionally, Santorum didn’t do much to eat into Romney’s delegate lead. (Romney could, in fact, still win the night, if not the narrative, by capturing the 26 combined delegates in Hawaii and American Samoa, where polls closed at 2 a.m. ET. And he did manage to salvage a win in the night’s two Pacific island contests by being victorious in the Hawaii caucuses and won the support of all nine delegates at the GOP caucuses in American Samoa). But the wins restore the spotlight that will allow Santorum to retrench and raise money, while robbing his rivals of triumphs they badly wanted.

Romney’s camp hoped a victory in the Deep South would dispel the obstinate fact that he has struggled to win over the staunchly conservative, Tea Party and Evangelical voters who form the crux of the GOP base. Exit polls showed Romney ahead in Mississippi, by many measures the most conservative state in the Union–81% of voters described themselves as Evangelical or born-again–and pundits crowed that a win in the reddest of red states would suck the last vestiges of drama from a race that now looks certain to drag on indefinitely.

For Gingrich, winning in the conservative heartland was not a luxury but a necessity. Pigeonholing himself as a regional candidate, the former House Speaker indicated after his win in Georgia that he expected to capture both Deep South contests. “From Spartanburg all the way to Texas, those all need to go for Gingrich,” said the candidate’s spokesman, R.C. Hammond, who said Newt needed victories in both states to remain a credible contender for the nomination.

In recent days, as surveyes showed the three candidates locked in a near dead heat, the Gingrich camp furiously backpedaled from those statements. Advisers released a strategy memo that framed the race as only now nearing “halftime.” But Gingrich has less than one-quarter of Romney’s delegates and has proven a less formidable national candidate than Santorum.

In the coming days, Gingrich is likely to be bombarded by a steady stream of back-channel pressure, as conservatives eager to clear a path for Santorum urge him to bow out of the race. Which is why Tuesday night’s results were doubly bitter for Romney, who was not only denied a huge symbolic victory but also may lose the benefit of the fractured conservative vote that has been his saving grace.

Both Mississippi and Alabama tracked with the demographic patterns set by their primary predecessors. Santorum won a plurality with very conservative voters, Tea Party supporters, those earning between $30,000 and $100,000, the outsize Evangelical communities (some 80% of Mississippians described themselves as born-again, as did 75% of Alabamans) and voters who said religious beliefs mattered “a great deal.” He vacuumed votes in rural precincts and held down Romney’s margins in the more moderate population centers where Romney has performed best throughout the primary cycle.

Once again, Romney patched together a coalition of affluent, exurban moderates who prized electability. He did well with elderly voters and Republicans leery of the Tea Party. Exit polls suggested that after scoring in the mid-20s with Evangelical voters in three previous Southern primaries, he did a little better this time: in Mississippi, he registered 29% with that cohort, according to CNN exit polls, which again lagged behind Gingrich and Santorum.

Santorum’s doubleheader sweep is certain to prompt a torrent of breathless hyperbole about his ascendancy and Romney’s lingering weakness. It was an impressive night for the Pennsylvanian, who has now added a trio of Southern states to his column. But from a mathematical perspective, his grand conquest changes very little. Romney still boasts a hefty lead and remains the only candidate with a legitimate shot at accruing the 1,144 delegates required to sew up the nomination before Tampa. “There will be no ground our opponents have made up,” said Romney aide Eric Fehrnstrom, who called the contests an “away game” for Romney.

The asterisk in that assessment is Gingrich’s future. Speaking Tuesday night in Birmingham, the former Speaker sounded defiant, stressing that he would plow forward toward Tampa. “I emphasize going to Tampa,” he said, because the evening disproved proved the media’s coronation of Romney as the “inevitable” nominee. “If you’re the front-runner and keep coming in third, you’re not much of a front-runner,” Gingrich declared. It’s a snappy zinger, but overall Gingrich is the guy in third.

Whether Gingrich’s ego will trump his grasp of math is the question looming over the race over the next week, as the candidates eye a clash in Illinois. “After tonight, it’s going to be a two-person race. It’s going to be Rick and Mitt,” said Alice Stewart, Santorum’s spokeswoman. That would make Romney’s road tougher, but he’s still the one with the inside track to the nomination.